One thought: if you have the RD-M8050 RD, I'd consider buying an XT M8070 FD. I have tried this specific combo ( again, borrowed stuff) and can confirm it works perfectly with our 8050 road levers, 11-40 XT cassette and 28/46 chainring combo. That specific derailleur is on closeout at universal cycles for $50 currently, which is a screaming bargain.
I specifically shied away from the MTB FD only because I was unsure if I could get it adjusted inward enough to shift into the small ring. I was also considering that the official Shimano capacity for that FD was 10t, but of course Shimano are notoriously conservative in their published specs. Seeing you tested it with an 18t difference, 16 in theory should pose no issues for us. I may just go ahead and purchase it with the FD905-L clamp, since I was already eyeing the Bottle cage mount for using one of the spare internal batteries I’ve got on the bench and eliminating the Junction B box.